vreeland



April 17, 1926. 1,666,518

F. K. VREELAND RADIO FREQUENCY AMPLIFIER Original Filed Aug. 6, 1923 2 Sheets-Sheet l Snowdon MKM www2@ w/M April u, 1,928.

Original Filed Aug. G. 1923 F, K. VREELAND RADIO FREQUENCY AMPLIFIER 2 Sheets-Sheet 2 MKM and the -mutualz capacity of "the: Coils by the shortest possible route. Other bridging condensers suchas Cb may be used when desii-ed to-bvpass` theoiitput current of 'one tube a'ndtlieinput-current of the' nextto the filament or ground bus.

The preferred arrangement shown' inFi'r'ziiicalf possessesnin.` astaticfeature-wherebythe external field of the transformer is prece. tically elimina-ted. 'In this arrangement each omthe: .coils-'of the transformer fis `made in twmsectionsfwound or connected in opposite directions se `.thal'ntheir external tfields oppose andi-neutralize each other, .as-.fully explained. in"die/application.above.mentioned.A .The infsvention isznot, limitedfto the' .use of,any.p ag, ticularffccnstructioniof .transformers.or. .oonplingeoi-ls.orfcouplingfthertnbes=of the-.suc-` ces'siyge-anipliersnnits,altlionglil prefer .to employva .-transformer..coupli ng Io f,tlie type: here described-,and .illustrated,. Wliiclig,pro.

n. preferalsp .to` employ. the. coiipling.:coils.

' Senne--nuphne-means....Whmoupling means, auf A5 0- providing;h .considerable latitude 'in ille' combined eroveral1 band .charac- ,'Tl'iii's :by .Winding ,theY transformer eoilswitlijow- .resistance thelapparatus. may. hel'inade liiighljrlselectivmso, that :the transformez; circuit,with. its inherent and associated capacitiesis resonant to a definite frequency and thc-'amplification is liigliior this frequency bntlower for vany other frequency. Tlie individual characteristic oni-veci such an amplifier unit is 'shown at aF Fig. 3 in which the ordinates represent. the ratio .of amplification and tlieabscissas represent the frequency. On tlic other hand, where an amplifier is desired .which works .effectively-over a wide rangenf frequencies I prefer to wind theitransform'er coils or particularlytliesecondary coil of' relatively high resistance; for examp1e.'b f winding them of fine. copper or larger German silver wire. This resistance. ha's'thetfectof lowering the-peak fof the amplification c'nrve without greatly lowering its 'amplitnde at ,frequencies dilieint from.

the-peakfrequencyl so .that a broad characteristic isY secured without corresponding loss. ini'ctlciency, .as shown for example. in 'b" Tli'e'f degree of coupling. between the coils is 'alsogan important factor in determining sired 'prefer to make1 theV coupling as close dueesfaisys'temlggreat.stabilityiand freedom the r.'

as prgicticable; lVliere a. sharply Selective characteristic is desicd a looser coupling is permissible, By suitably proportioning the duetenee 4hande-thee mutual capaci-ty o.- the windingsgutlie l characteristics of the amplifier units "m'av'ibe determined at will.

s A suhstantiially iiatcoinbinederover-fallfaniple, Figure 3 at c5 shows' a. typical charac- .terstieiofa iireefstage,band amp1ier. The' curves in broken li'rieshl 2,3 sl1ojv-.the.. eliar.,. ..a-ctcristics of. .the ,thi-eel individual ,units,

. cludin'g'l; tubes. i andI transformers. foi-. other;

t coupling means that are connected in cascade',

while. the full/linemurve Lt-represents the re- ,.sulta'ntg or. ovcrallban I coixilvfifiied isystcma..

d Characteristic of the.

.Timmeren ei-limitarse@ f. .ihr vidual liinits 'of :L band amplifier-5 I rlY beide-I.

shunt-inganexternal condenserr across the.' outer terminals 'o tlieprin'iary and `seeonz1- ary .'coils' p, s. exteri'ial capacity lis in .eilect added ,tothe inherent mutualcapac'ityiuu of tlic. coils,l und so lowers tlie"freq1 iency .cliaxaeteristic..A Tlie' second "-:irrzingement consist-s in connecting 'condenser 9 in par. 'aille-l witli'llie. primary coil p.; This has :i result equivalent-(n increasing the ei'e-.clive indue-'tance of the'prin'iary coil and couse. .qucntly it lowers the frequency eliaractcriw ...tie A `similar result is obtainedby-connecting a condenser 10 across thosecondary coil s but the elect ofsuclreapacity is pi'opo.1- tioiiatclygrcater than when .tlie.vsaino. .ca pzicty'is added at 9 if,.as1 prefer, the trnnsformer. coils 7),;6' have a step-pp .rat-io.

The',condensers or. capacities S. 9,110 may he used singly or in anydesired .combinationamd any. on all, of tlieniniay be made variable. An .effective:arrangement ,'for tun:

designlngthe transfprnieeto linvca sharply. ,selectivo e ,characteristic andv .inserting .a "variablexondensen Figure.. l" i shows-such variableapacitiesat.8, 9, 10and Figure. l

gle operation, as shown n Figure 1. These lll.'

in i r the coupling transformers is secured by illustratesh specifically `the. locationo. the

I `pr,efe1. .-to effect, .thiszadjiistment .ottliej several transformerspthe, system by a sinsuccessivelyncross thepijinlary coils. o f 'the7 transformers, thoixglrit vv'ill'be understood .-thatgthe fcapacitiesmay added in any of arranged-1m :bi-aperte@ multicast., for.

werden -orginatgfslwnaf-.at @ne Pet di rlapgemepthasnilierous ativan- A ,have a centralyalley. Usually the optimum spacing -is` secured.' Afor` -stage amplifier when the high and low'frequency characterfercncegfrom signals, of 11ndesirc d ,frequen cies-,sincethe amplifier is, hi h ,ly effective for-frequences .wit iinitsgban: but excludes hand. J3y this .means egtremely .feeble sig- --..nals may be received without..1nterference from the most, powerful nearby-stations. The flat-nessof the band p fgeifectiyc amplification aud the sharpness of thc cut-off for frequenciesg outside'this band, 'which characterize the preferred form of my mvention, are secured by so relating the spacing ofthe characteristics nf the. several arnplifier stages to the width and form of the characteristics as to secure the particular overlap that is required for the characteristic employed. This relation is illustrated in Fig. 3, c, which shows curves for a threestage amplifier.

Considering the relation of these curves at different frequencies, it is notedthet for a frequency less than the peak frequency of the characteristic 1, characteristic 3 shows choseeithsths .bandapealced. If the spacing ishroader than the division 'df-this int aplurality of narrower hands is-useful in eliminating interalmost completely 'frequencies outside of this substantially no amplification and the overall characteristic is small. As the frequency is increased, 'all the component characteristics are increasing simultaneously, und thc amplification' rises very'sharply up to a frequency correspondingto the peak of curve 1. At this `frequency curve l begins tn fall while the others rise more slowly, and, by virtue of the particular spacing employed, the rise of one curve substantially offsets the fall of another, so'tlult the nmplication is substantially uniform, up to a point corresponding approximatel)1r to the peak of curve 3, beyond'wliich all of the curves are descending. The resultant characteristic descends WiL-h avery sharp cutndtcd'tliat ivhile all the com- -pon'e'r'it cllaracteristics are selective, their'cutver. f12: iSim-lerlrthelswltshes S',- Sii-ST1 rate simultaneously. When the' switches olf gradual in' the inann'er'that is usual in bandA chai-,acteristic 4, however, the cut-ofi is, sha rpf miic h sharper than the slope of th e co`m O nent haracteristics-so that the width zo' Athe' ':ur'vc at its' b 'ase `is `not matcrially greateifthan that of the component characteristics, notwithstanding the breadth This'isof great importance since it p'eroptiniuni, fthef o ver-a'll characteristic will istics (3 and 1,'Fig. 3, c) intersect and ovcr- 105 lap at point corresponding; tn about half the maximum -amplification. For other ampliicrs the optimum spacing is readily determined by computation or graphic methods.

I Claim as my invention:

l. In 'an amplifier for high frequency eurrcnts, a. plurality of am lificr tubes` coupling means connecting ticse tubes in cascade, the severa-l coupling mcanshaving frequency characteristics which are difieren(- for the. several componentamplifiers nud so related to each other that the combined amplifying effect of the syst-em is substantially uniform over a givenhanil of frequencies, and means for simultaneously adding reactances to the coupling menus, thereby shifting the frequency relation of the amplification hand while preserving its uniform hand character.

2, In an amplifier for high frequency currents, a plurality of amplifier tubes, inductive coupling means connecting,r these tubes in cascade, the several inductive coupling means having frequency characteru' 

